Various firearms, and particularly assault rifles, have been designed to include a collapsible stock. In general, such firearms include a buffer tube on which the collapsible stock is axially slidable. Some mechanism is typically included on the stock to fix its axial position on the buffer tube to allow the user to quickly adjust the effective length of the stock.
One example of such a firearm is the M-4 rifle. The M-4 is a widely used and popular rifle, and users value the ability to rapidly adjust the effective length of the stock. However, problems experienced with the collapsible stock of the M-4 rifle can be illustrative of shortcoming of current designs.
For example, while the axial position of the collapsible stock is maintained relatively securely, clearances between the stock and buffer tube often result in a loose, wobbly feel—particularly when the collapsible stock is in the fully extended position and a relatively small portion of the buffer tube is engaged within the collapsible stock. This loose, wobbly feel can be distracting to the user and adversely impact marksmanship.
This type of fit problem can be exacerbated when, as is the case with the M-4 rifle, models of a given rifle are available with varying buffer tube diameters. A collapsible stock dimensioned to accommodate larger buffer tube diameters will tend to be excessively wobbly on smaller buffer tube diameters. On the other hand, a collapsible stock dimensioned to more closely accommodate smaller buffer tubes may not fit on larger buffer tubes, at all.
Additionally, with repeated cycling of the collapsible stock assembly, wear of the stock assembly (typically plastic) against the buffer tube (typically metal) will increase clearances. Accordingly, the fit problems can become worse over time.